3GPP LTE and LTE-Advanced are one of the next generation cellular communication standards, which create a new series of specifications for the new evolving radio-access technology. In LTE-Advanced, heterogeneous network (HetNet) is deployed by including Macro eNB/eNodeB and low power nodes (LPN) such as pico eNB, femto eNB, relay node and RRH. The low power nodes increase the spectrum efficiency and improve the system coverage and cell throughput performance, but introduce interference cases which do not exist in a homogeneous network.
One of the interfering cases is, for example, the interference from a Macro eNB to a user equipment (UE) served by a low power node, especially when Cell Range Extension (CRE) is applied. To eliminate such kind of interference, an Enhanced Inter-Cell Interference Coordination (eICIC) scheme is proposed. Specifically, the eICIC scheme introduces two kinds of subframes, one is normal subframe and the other is non-normal subframe, e.g., an almost blank subframe (ABS), non-zero power ABS, and so on. In the eICIC scheme proposed in LTE Release 10, the Macro eNB will stop transmission in the ABS, so interference from the Macro eNB to the UE will be substantially reduced during the ABS. In Further eICIC (FeICIC) scheme proposed in LTE Release 11, the non-zero power ABS is introduced to further improve the performance. In particular, the Macro eNB will not stop transmission in the non-zero power ABS, but the downlink transmission power is decreased so as to reduce the interference from the Macro eNB to the UE. Therefore, the interference levels for the UE in normal subframes and in non-normal subframes are different.
Another one of the interfering cases is the interference from a LPN (e.g., pico eNB) to a UE served by a Macro eNB. In an exemplary eICIC scenario, the LPN stops transmission in the ABS, and the UE experience no interference from the LPN during the ABS. In another exemplary eICIC scenario, the LPN decreases transmission power in the non-zero power ABS, and the UE experience small interference from the LPN during the non-zero power ABS. Therefore, the interference levels for the UE in normal subframes and in non-normal subframes are also different.
Yet another one of the interfering cases is the interference from a Macro eNB to a UE served by another Macro eNB. Similarly, under the eICIC scheme, the interference levels for the UE in normal subframes and in non-normal subframes are also different.
Modulation and coding schemes (MCS) describes a number of variables need to be agreed upon between the transmitter and receiver, including coding method, modulation type, number of spatial streams, and other physical attributes. The MCS value or index is used to establish the communication variables a transmitter and receiver will use. The MCS index can be used to determine the corresponding physical data rate.
In order to improve transmission efficiency, mobile communication solutions use various advanced techniques so that the transmitter to adjust the data rate according to the channel quality or condition. Such solutions receive Channel Quality Information (CQI) fed back from the receivers and perform data transmission at an optimal timing with an optimal MCS. Specifically, these solutions may decrease the data rate for bad channel conditions so as to maintain a reception error rate at an intended level and increase the data rate for good channel conditions to maximize the throughput, thereby improving system throughput. In this regard, the transmission efficiency may be improved with the enough information on the transmission channel.
However, due to the different interference levels for the normal subframes and the non-normal subframes in the eICIC scheme, the MCS applied to the normal subframes may not be suitable for the non-normal subframes; accordingly, the performance of the system will be reduced.
In view of the foregoing problem, there is a need to find a suitable MCS for the non-normal subframes, so as to effectively improve the scheduling of the UE and the performance of the system.